please explain specs

[icarus]

The majority of Speaker specs I understand completely, there is just two that have me a little stumped. They are Sensitivity, and nominal impedance. we'll start with sensitivity, when they refer say 91db, or 88db (for example) what does it mean and how does it affect performance, and sound quality. As for nominal impedance, what is it refering to and how would an impedance of 8ohms perform compared to 4ohms?

if anyone could answer this, you would just make my day haha

[Dusty Chalk]

Sensitivity, in a nutshell, is how loud a speaker will go for the same amount of wattage. Lower sensitivity speakers aren't as loud as higher sensitivity speakers for the same amount of watts, and therefore usually need higher power amplifiers. Once you get beyond a certain point, it's not so much that they need the watts, it's that the distortion in your amplifier becomes audible.

Impedance is the load that the speaker presents to an amplifier. Low impedances approach a short circuit, high impedances approach an open circuit, both of which are bad for amplifiers, which is why speaker manufacturers and amplifier manufacturers long since agreed on the 4 ohm and 8 ohm nominal standards. High impedances aren't generally as bad for most amplifiers, in fact, some tube amps actually work better with higher impedance loads (E.G. 16 ohm nominal). But due to the math, the amplifier usually produces significantly fewer watts for those higher loads, so it's a trade-off.

As to how both effect performance and sound quality -- well, that's the question, now, isn't it? There are some people who swear by high sensitivity speakers, but I tend to think of many high sensitivity speakers as "fragile" and not being able to go as loud, so I guess it depends on how large a room you're trying to drive. I could be wrong about that though -- JBL's are high sensitivity and go loud well.

For the most part, it's a matter of trade-offs. You do need to keep these things in mind -- for example, if you want to hear everything an amp has to offer which has no negative feedback, and utilizes a single-ended design, you will almost always have a low-wattage amp, so you will want to have a high-sensitivity speakers. But if you want to hear everything a ribbon-based speaker like the Apogee has to offer, then many of those speakers have a tendency to have an amp-killing impedance (impedance is frequency-dependent, so when they say it goes down to 1 ohm, they mean at certain frequencies), so you need to have an amp that can take those low impedances, like the Musical Fidelity kW series, which claim to be able to drive anything with essentially no distortion, due to their ability to basically generate enough current across their speaker terminals to kill a small animal.

[icarus]

wow dusty thats probably the best explanation I have gotten from this site so far.. truly greatful thanks.

[Florian]

But if you want to hear everything a ribbon-based speaker like the Apogee has to offer, then many of those speakers have a tendency to have an amp-killing impedance (impedance is frequency-dependent, so when they say it goes down to 1 ohm, they mean at certain frequencies), so you need to have an amp that can take those low impedances, like the Musical Fidelity kW series, which claim to be able to drive anything with essentially no distortion, due to their ability to basically generate enough current across their speaker terminals to kill a small animal.

Welcome to my world :cornut: Good explenation. Just for the infos sake, the Apogee scintilla is always 1ohm. Doesnt rise above so its a serious pig to drive.

[GMichael]

Welcome to my world :cornut: Good explenation. Just for the infos sake, the Apogee scintilla is always 1ohm. Doesnt rise above so its a serious pig to drive.

Do the lights dim in your town when you power up.

Great explination Dust.

[Florian]

Do the lights dim in your town when you power up.

Great explination Dust.

Actually the very first time i fired them up, i killed the entire house fuse. Thats why i need 6 dedicated 20 amp circuits. Weee ;-) The lights only dimm when turning one Krell on. :ihih:

[GMichael]

Actually the very first time i fired them up, i killed the entire house fuse. Thats why i need 6 dedicated 20 amp circuits. Weee ;-) The lights only dimm when turning one Krell on. :ihih:

Hey,

Did you ever read this? It's from AH. It makes me think of you and RGA. I didn't write it or claim to. Just funny as h.ll!

Sorry to jack this thread. But I do think that the question has been answered.


My First Audioholics Anonymous Meeting...

It was about time I attending my first meeting. Three interventions and an ultimatum from my wife finally convinced me to go. Held in a library (no loud noises allowed), the group was a hodgepodge of men and women, all nearly broke from spending every penny they have (and many they don’t) on equipment upgrades. In this group, I discovered that not only was I not alone, I wasn’t even the worst one.

I wandered outside just to be besieged by two of the long-time members. It was clear they were far from “cured” but they had stopped spending… as much. I remembered their names from the meeting. Bob was a short man wearing a noise canceling headset and a large hat, and therefore, spent a lot of time yelling. He was flanked by Sid, a tall, lanky man who apparently didn’t mind Bob yelling at him all the time. I soon found out why.

Bob: HEY THERE, NEW GUY HUH?

Me: Yeah.

Sid: What?

Bob: WHAT?

Me: YEAH, I’M NEW.

Sid and Bob: WHAT?

Me: OK, THIS IS GETTING ANNOYING, BOB I GET, BUT WHAT’S YOUR DEAL?

Sid: Oh, I like to listen to things loud; you should really check out my system - it ROCKS!

Me: Ok, I wouldn’t mind that…

Bob: IF YOU SAID YES, MINE IS FIRST. IT IS WAY BETTER THAN SID’S LAME SYSTEM.

Which quickly degenerated into a heated argument. Never one to pass up an opportunity to experience someone else’s idea of sonic bliss, I jumped into my car and followed them to Bob’s house. Bob’s home, as he explained to me, was chosen specifically because it had a room with the proper room dimensions (1:1.4:1.9). It happened to be the only bedroom but Bob didn’t seem to mind sleeping on a cot in the kitchen. The door to the adjoining bathroom was drywalled shut, and the frame of the main door to the room was lined with rubber to prevent vibrations. The room was treated with rigid fiberglass and membrane absorbers, diffusers, and bass traps but only at very odd locations. Inside the room were five of the hugest horn loaded speakers I’d ever seen. Nary a sub in sight.

Each of the speakers was placed equidistant in a circle configuration pointed at a purgatorial looking wooden chair in the center with an odd looking metal contraption where the headrest should be. Bob put his finger to his lips indicating quiet and took off his headset and hat. At once, I realized why he wore the hat. At four points around his head, he had surgically installed metal fittings. At first not understanding, I saw Bob sit in the seat and place his head in the metal contraption that connected to the metal fittings, locking his head in place.

Whispering, Bob commented, “This is the sweet spot. I’ve designed the room so that at this exact spot, a person can experience audio nirvana.”

“Where’s your…” I started.

“AHHHHH!” Bob screamed softly. “Not so loud!”

“Sorry,” I whispered, “where’s your gear?” Bob pointed to a shoebox next to the speaker directly in front of him. Approaching, I noticed that there were wires running from it. I opened it and saw five of the smallest little amplifiers connected to a 9 volt battery and an MP3 player. “What the…” I began.

Bob interrupted, “Yep, that’s my whole rig,” he whispered with a smile. “One watt amps and a modified MP3 player that oversamples each track so many times that it can only hold three songs. My copies are better than the original recordings. My speakers are so efficient that I could play this system 24/7 for a week before having to change the battery!”

Bob hit a button on his remote and the cacophony that escaped the speakers was completely without soundstage, imaging, or dimension. The room rang, vibrated, echoed, and just about everything else you could think of. I glanced at Bob and noticed the satisfied smile on his face. After a moment, he freed himself from the contraption and offered me his seat. Skeptical, I sat.

Honestly, it sounded pretty good, quite a bit better than my set up… though only in one spot. Bob was a good deal shorter than me, so I had to slouch down to get my head in the proper location. Once there, as long as I didn’t move or breath or anything, it sounded great. If I turned my head or nodded, the soundstage was completely destroyed. Bob’s smile increased as he saw me get into the right location, “See,” he whispered, “it’s perfect!”

It was at this point that Sid had had enough; he stormed in sending Bob diving for his noise canceling headphones. “Alright, let’s go,” he demanded, “time to experience a real system.” Luckily, Sid didn’t live too far away, but it wasn’t exactly a good neighborhood. Well, it was more of an industrial complex. Sid had apparently converted the top floor of an old factory into an apartment. Inside, it was one big open room except for what looked to be a huge square vault in the center.

“What’s that?” I asked.

“What?” Sid replied.

“WHAT’S THAT?” I yelled.

“Oh, that’s the room,” he smiled.

Square? I thought. After what Bob had explained to me about room dimensions and modes, I was confused why someone would build such a room. Giving him the benefit of the doubt, I watched as Sid hit a large button on the wall of the “listening room.” A loud whoosh escaped as a large door began to retract from the wall on a boom that sat flush to the wall. An alarm sounded causing me to involuntarily duck from the expected air strike. The boom arm pulled the door out, and out and out. First about a foot of solid steel, followed by two feet of insulation, and finally acoustical foam in the shape of large pyramids with the apexes pointed into the room. Sid smiled from ear to ear, “Now that is what I call room treatment!” he exclaimed.

Sid motioned me in and I entered hesitantly. Inside, I felt like my ears needed to pop or as if I had balloons on either side of my head. The room was eerily quiet – my breathing seemed an affront to the unnatural silence. Five large bookshelves speakers were sitting on top two subs pointed generally toward a couch in center of the room.

Upon closer examination, the two subs turned out to be one sub and one VERY LARGE AMP. Once again, Sid smiled and explained, “Two channels each, 5000 watts per channel. The sub is a passive 17” ported design I came up with myself. This system will hit 142 dB at 3 Hz!”

Looking around, I queried, “Where is…oh yeah, WHERE IS YOUR EQUIPMENT?”

Bob pointed to a small black box with a red blinking light on it. Incredulous, I was going to take a closer look when Sid led me out. Once the door was sealed, Sid hit the only other button on the outside of the room. Suddenly the lights dimmed, the streetlights went out, and somewhere a sun died. After a moment, the room started to vibrate, the walls flexing in and out. I could feel the bass in my stomach and my ears started to ring. Next to my head, a fly exploded. Sid nudged me with his elbow, “That’s LOUD, baby!”

“WHY ARE WE OUT HERE?” I asked.

“Oh, we can’t go in there, you’ll go deaf,” was the reply.

“SO WHY DON’T YOU TURN IT DOWN?”

“Hey man, that’s 5000 watts all channels driven! You can’t get that anywhere else. I paid for all those watts, damn if I’m not going to use them.”

“WHAT’S PLAYING IN THERE ANYWAYS? TOOL, METALLICA?”

“Oh, that’s just a sine wave. It is the only way to use the amps and the speakers to their full potential.”

Bob and Sid sure were nice. I’m not sure they have fully optimized their systems yet, but it seems to work for them. For me, I’m thinking I need to spend less time at Audioholics Anonymous meetings and more time with the wife and kids. Those guys are crazy!

- Tom Andry

http://www.audioholics.com/news/editorials/AudioholicsAnonymous.php

[Florian]

That is really a classic! I love it. We all really have different tastes, and some have none but its all good :cornut:

Thanks for posting!

[E-Stat]

As for nominal impedance, what is it refering to and how would an impedance of 8ohms perform compared to 4ohms?
Let me emphasize the word "nominal" in that the stated value is for a single frequency or range only. Most speakers (with a few exceptions like Magneplanars) vary their impedance by frequency. The curve for some speakers looks like a roller coaster. This is important for amplifier selection. I favor tube amps, but because of their high source or output impedance, their frequency response can be affected by those roller coaster curve speakers. While my 'stats are kinda evil at the top, they exhibit a pretty smooth curve that does not vary radically from octave to octave. On the other hand, look at this speaker:

Roller Coaster (http://stereophile.com/floorloudspeakers/1205bw/index4.html)

So, is this a 3 ohm speaker? 6? 12? 20? Solid state amps tend to work better with this kind of speaker to maintain a neutral response.

I agree with the opinion that neither spec in and of itself provides any qualitative information. They do provide insight to matching an amplifier to your chosen speaker. This topic is crucial and often overlooked. The "best" amplifier for one speaker may not be the optimum choice for another.

rw

[Pat D]

The majority of Speaker specs I understand completely, there is just two that have me a little stumped. They are Sensitivity, and nominal impedance. we'll start with sensitivity, when they refer say 91db, or 88db (for example) what does it mean and how does it affect performance, and sound quality. As for nominal impedance, what is it refering to and how would an impedance of 8ohms perform compared to 4ohms?

if anyone could answer this, you would just make my day haha
Sensitivity is usually voltage sensitivity, measured with a 2.83 volt signal, with results given for a 1 meter distance in front of the speaker. That's usually too close to properly measure a speaker, so the sensitivity is usually based on how loud the speaker plays from a greater distance and converted to a 1 meter distance so that the results can be compared.

The impedance of most speakers varies with frequency and speakers are not wattage sensitive but voltage sensitive (really square of voltage sensitive). The actual wattage calculated for the same level of signal for different frequencies would vary because the impedance at those frequencies is different.

That seems simple enough but there is no standard way of doing the measurements. Reviewers usually use filtered pink noise and I think many manufacturers do, too. Pink noise has the same energy for each octave. It is also usually filtered to cover less than the whole audible range to something like 500-2000 Hz, or maybe 200-5000 Hz so as to correspond more closely to how the ear perceives loudness (hearing is less sensitive at low and high frequencies). Soundstage magazine and some speaker manufacturers use the anechoic chamber at the NRC to measure speakers, and here is an explanation of what some of them mean. Sensitivity in under Chart 1, No. 4:

http://www.soundstagemagazine.com/measurements/test_loudspeakers.htm

But not everyone uses an anechoic measurement. Klipsch would argue that since speakers are actually heard in a reverberant field at home, then their senstivity is properly measured in a reverberant field. This is not dishonest, but it does mean that one needs to subtract about 4 dB from Klipsch's sensitivity figures to compare them to the figures for other speakers--but you know, the Klipschorn still comes out at 99 DB sensitivity that way, which is still very sensitive.

Some manufacturers give both figures such as 91/(88) for in room (anechoic).

Then some manufacturers give sensitivity figures based on who knows what--there is no mandated standard way of doing them.

Impedance specifications are seldom communicative of very much. I suppose an 8 or 6 ohm nominal impedance rating would mean the manufacturer thinks most receivers and amplifiers would drive them OK. A 4 ohm rating would mean that the receiver or amplifier should have a moderately robust power supply so as to be able to supply the amperage required. But if you actually look at the impedance vs. frequency curve of many speakers, you will likely find that many of them get down to 4 ohms in the midbass region, where there is a lot of musical energy on many recordings. Again, some manufacturers will provide a minimum impedance rating, and I would go by that rather than some nominal rating. I would consider this to be a 4 ohm speaker, for example, as the impedance gets below 4 ohms in the mid-bass/lower midrange area, a fairly energetic range.

The Paradigm Studio 20 is a nice little speaker and is spec'd rather vaguely as "Compatible with 8 ohms:"

http://www.paradigm.com/Website/SiteReferenceProduct/RModels/StudioSeries/StudioSpecs.html

However, the actual measured impedance gets down to around 4 ohms:

http://www.soundstagemagazine.com/measurements/paradigm_studio20_v3/

But it's moderately sensitive and is not really a very hard speaker to drive.

So, manufacturers specifications often have to be take with a grain of salt, although many are generally pretty honest about it.

Now, what have these to do with sound quality? Well, not much. Sensitivity and impedance are more useful for determining what sort of amplifier is needed to drive them properly. But at the sorts of levels many people listen, a good receiver will work with a great many speakers. But it's nice to have a big amplifier.

Sound quality in speakers has more to do with frequency response and dispersion characteristics.